This invention relates to the use of microwaves for the treatment of prostate disease and, more particularly, to catheters designed to efficiently irradiate the prostate of a male patient with microwave power.
As known in the art, prostate disease, such as prostate cancer or benign prostatic hypertrophy (BPH), inter alia, results in a narrowing of the urethra in the neighborhood of the prostate caused by the surrounding enlarged prostate. This narrowing restricts the passage of urine. As is also known, a diseased prostate can be treated by irradiating prostate tissue with an amount of microwave power sufficient to heat that prostate tissue to a therapeutic temperature. However, the maximum microwave power that can be used is limited by the fact that it is essential that none of the prostate tissue be overheated beyond a maximum therapeutic temperature and that none of the irradiated non-prostate tissue be heated beyond a maximum safe temperature (which maximum safe temperature for non-prostate tissue is below the maximum therapeutic temperature for prostate tissue).
Catheters designed to be inserted into the urethra that help pass urine and bulb applicators designed to be inserted into the rectum of the patient, which have been fitted with a microwave antenna, have been used in the past to irradiate the prostate tissue of the patient with microwave power. A urethral catheter is often equipped with a so-called Foley balloon located close to the tip thereof, which may be inflated (usually with air) after the tip of the urethral catheter has been inserted into the patient's bladder, thereby to secure the catheter at its fully inserted position within the patient's urethra. A bulb applicator may be made non-symmetrical so that, after full insertion into a patient's rectum, the microwave power preferentially irradiates the patient's prostate tissue.
Regardless of whether the patient's prostate tissue is irradiated with microwave power radiated by the microwave antenna from the patient's urethra or rectum, it is apparent that non-prostate tissue situated between the patient's prostate and urethra or rectum, as the case may be, also will be irradiated. Further, since the microwave field intensity tends to vary as an inverse function (e.g., as an inverse square) of distance from the microwave antenna, this non-prostate tissue will be more highly irradiated than will the prostate tissue (particularly that prostate tissue situated more distal to the microwave antenna), because the irradiated non-prostate tissue is more proximate to the microwave antenna. Therefore, the difference between the respective microwave-field intensities heating the more proximate irradiated non-prostate tissue and the more distal irradiated prostate tissue varies as an inverse function of the ratio of their respective distances from the microwave antenna. Thus, in order to heat the more distal prostate tissue to a higher therapeutic temperature without concurrently either overheating any of the more proximate prostate tissue or heating the more proximate non-prostate tissue beyond a maximum safe temperature, it would be desirable to increase the minimum distance between the microwave antenna and the more proximate non-prostate tissue, without appreciably affecting the distance between the more distal prostate tissue.